parser: support split base,index effective address

parser: support split base,index effective address

Mostly intended for the "mib" expressions in BNDLDX/BNDSTX.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Jin Kyu Song <jin.kyu.song@intel.com>

• [DBH] parser.c
• [DBH] test/splitea.asm